arXiv subjects

Sanjoy Datta

Publications and source records attributed to Sanjoy Datta.

23 records · Page 2Linked to original sources

arXiv2011

Thermally Fluctuating Inhomogeneous Superfluid State of Strongly Interacting Fermions in an Optical Lattice

The presence of attractive interaction between fermions can lead to pairing and superfluidity in an optical lattice. The temperature needed to observe superfluidity is about a tenth of the tunneling energy in the optical lattice, and currently beyond experimental reach. However, at strong coupling the precursors to global superfluidity should be visible at achievable temperatures, in terms of fluctuating domains with strong pairing correlations. We explore this regime of the attractive two dimensional fermion Hubbard model, in the presence of a confining potential, using a new Monte Carlo technique. We capture the low temperature inhomogeneous superfluid state with its unusual spectral signatures but mainly focus on the experimentally accessible intermediate temperature state. In this regime, and for the trap center density we consider, there is a large pairing amplitude at the center, spatially correlated into domains extending over several lattice spacings. We map out the thermal evolution of the local density, the double occupancy, the pairing correlations, and the momentum distribution function across this phase fluctuation window.

cond-mat.quant-gas↗

arXiv2009

Supersolidity in a Bose-Holstein model

We derive an effective d-dimensional Hamiltonian for a system of hard-core-bosons coupled to optical phonons in a lattice. At non-half-fillings, a superfluid-supersolid transition occurs at intermediate boson-phonon couplings, while at strong-couplings the system phase separates. We demonstrate explicitly that the presence of next-nearest-neighbor hopping and nearest-neighbor repulsion leads to supersolidity. Thus we present a microscopic mechanism for the homogeneous coexistence of charge-density-wave and superfluid orders.

cond-mat.str-el↗

arXiv2008

Quantum phase transition in Bose-Holstein model in two dimensions

We derive an effective d-dimensional Hamiltonian for a system of hard-core-bosons coupled to optical phonons in a lattice. Away from half-filling, we show that the presence of next-nearest-neighbor hopping in the effective Hamiltonian leads to a superfluid-to-supersolid transition at intermediate boson-phonon (b-p) couplings, while at strong-couplings the system phase separates. However, at half-filling and at a critical b-p coupling (as in the xxz-model), the system undergoes a superfluid-to-charge-density-wave transition without any signature of supersolidity. Our analyses is based on extensive calculations of the structure factor, the superfluid fraction, the Bose-Einstein condensate fraction, and the system energy at various fillings. We present a phase diagram for this system and compare it to that of the xxz-model. We also demonstrate explicitly that the next-nearest-neighbor hopping (in the absence of nearest-neighbor hopping) in the effective Hamiltonian leads only to a single transition, i.e., a first-order superfluid-to-supersolid transition.

cond-mat.str-el↗

arXiv2006

Phase transition and phase diagram at a general filling in the spinless one-dimensional Holstein Model

Among the mechanisms for lattice structural deformation, the electron-phonon interaction mediated Peierls charge-density-wave (CDW) instability in single band low-dimensional systems is perhaps the most ubiquitous. The standard mean-field picture predicts that the CDW transition occurs at all fillings and all values of the electron-phonon coupling $g$ and the adiabaticity parameter $t/ω_0$. Here, we correct the mean-field expression for the Peierls instability condition by showing that the non-interacting static susceptibility, at twice the Fermi momentum, should be replaced by the dynamic one. We derive the Luttinger liquid (LL) to CDW transition condition, {\it exact to second order in a novel blocked perturbative approach}, for the spinless one-dimensional Holstein model in the adiabatic regime. The small parameter is the ratio $g ω_0/t$. We present the phase diagram at non-half-filling by obtaining the surprising result that the CDW occurs in a more restrictive region of a two parameter ($g^2 ω_0/t$ and $t/ω_0$) space than at half-filling.

cond-mat.str-el↗

arXiv2005

Many-Polaron Effects in the Holstein Model

We derive an effective polaronic interaction Hamiltonian, {\it exact to second order in perturbation}, for the spinless one-dimensional Holstein model. The small parameter is given by the ratio of the hopping term ($t$) to the polaronic energy ($g^2 ω_0$) in all the region of validity for our perturbation; however, the exception being the regime of extreme anti-adiabaticity ($t/ω_0 \le 0.1$) and small electron-phonon coupling ($g < 1$) where the small parameter is $t/ω_0$. We map our polaronic Hamiltonian onto a next-to-nearest-neighbor interaction anisotropic Heisenberg spin model. By studying the mass gap and the power-law exponent of the spin-spin correlation function for our Heisenberg spin model, we analyze the Luttinger liquid to charge-density-wave transition at half-filling in the effective polaronic Hamiltonian. We calculate the structure factor at all fillings and find that the spin-spin correlation length decreases as one deviates from half-filling. We also extend our derivation of polaronic Hamiltonian to $d$-dimensions.

cond-mat.str-el↗